This invention relates to a transmission device for a bicycle internal gear hub and more particularly a transmission device for introducing a rotational shift movement into a internal gear hub.
A multi-speed internal gear hub includes at least one planetary gear mechanism that is arranged around a stationary hub shaft. Torque is transferred via a sprocket to a driver and further via one of the several transmission paths of the planetary gear mechanism to a hub sleeve. A particular transmission path is selected by components of a gearing system being rotating or displaced relative to the hub shaft. Gear selection is accomplished via a shifter located on or near the handlebars and is transmitted mechanically via a sheath cable or statically (e.g. electrically) to the multi-speed hub. A shift movement may be introduced into the internal gear hub by a shaft shifting device arranged on one end of the hub shaft. The axial shifting movement corresponds to the selected gear. With static shift transfer, mechanical conversion of the shifting signal is accomplished via an actuator.
Shift movements may be introduced into the internal gear hub linearly, e.g. by means of pushing or pulling elements, or rotationally. The shifting operation is generally guided from outside into the interior of the hub by means of a vertical component.
EP 0350791 discloses an introduction of a linear shift movement into the internal gear hub. Speed change members are located within the hub shaft and are in control connection with a gear system of the hub. The speed change members are either pushed inwards of a bore of the hub shaft or moved outwards under the action of biasing members. Each of the speed change members have a respective end portion adjacent one end of the hub shaft and thereby increases the axial dimension. This axial structure is sometimes felt to be troublesome, and should be minimized or eliminated.
Introduction of a rotational shift movement into the gear hub may be accomplished coaxially of the hub shaft and outside of the hub shaft. The rotary movement is directed into the interior of the hub via a rotating component mounted at both ends, or by means of a rotatable sleeve that engages fingers axially through cutouts in a control element.
An example of a rotational shift movement is disclosed in DE 24 58 871. The linear shifting movement is converted into a rotary movement by a cable spool and is transferred coaxially between two roller bearings into the interior of the hub. A disadvantage of this configuration is that the introduction and transfer of the rotational shifting movement is very complex. It is very complex because the rotating components lie in the power flow between the hub sleeve and the hub shaft and must transfer all the bearing forces as well as the forces resulting from brake actuation.
Another example of rotational shifting movement is disclosed in EP 0 383 350. The rotary motion of the cable spool is directed into the interior of the hub through cutouts of a control member rotatably mounted on the outer periphery of the hub shaft. This configuration only allows a limited rotation angle of the control member, thereby unfavorably limiting the shifting travel or shifting angle for each gear ratio. This results in unfavorable transfer conditions requiring large angles of inclination at sloped surfaces to transmit the shifting motion.
There is a need for a simple device that introduces a shift movement into the internal gear hub. An apparatus that eliminates the need for an extended axial width due to a shaft shifting device or complex implementation using bearing-mounted components and limitations on the rotation angle in the context of rotational transfer using cutout segments with dimensions predefined by functional factors.